1. Field of the Invention
This invention relates in general to acoustic noise reduction in a media storage system and more particularly, to active noise reduction for a hard disk drive.
2. Description of Related Art
As personal computers have proliferated in the work place and home, concerns have increased about their effect on the work and home environment. One area of concern is the effect of acoustic noise generated while the computer is in operation. A personal computer contains many different components, some of which generate acoustic noise. Examples of noise generating components include fans, hard disk drives (HDDs), and power supplies. HDDs in particular, operate at relatively high rotation speeds and are a large contributor to noise. HDDs are not only used in personal computers but are also used in personal television products (PTV), which are devices for recording broadcasted information, similarly to a video cassette recorder (VCR). Since a PTV is commonly located close to a TV, acoustic noise generated by the HDD becomes an important factor.
Typically, acoustic noise generated by the HDD can be attributable to two main sources, the spindle motor with it rotating disks, and the actuator with its voice coil motor (VCM). Contemporary HDDs are being designed with higher spindle speeds and faster access times for improving the performance of the HDD, however this improvement has resulted in increased acoustic noise.
Attempts to reduce acoustic noise generally follow one of two approaches. The first approach uses a sound absorbing material to surround, for example, the drive module to insulate the external environment from the noise generated by the HDD. One main disadvantage with this approach is that the sound absorbing material will generally provide heat insulation as well. As heat builds up in the HDD, the performance of the HDD can degrade. Another approach for decreasing acoustic noise is to increase the seek time of the HDD by reducing the movement of the actuator, which has the negative effect of decreasing the performance.
Active noise reduction is the second approach taken to reduce the acoustic noise. Typically, a microphone remotely located from the HDD receives undesirable acoustic noise and intended sound, then feeds it to an electronic circuit where it is phase-shifted 180 degrees, amplified, and broadcasted through one or more transducers, such as a speaker. Shifting the waveform of the receiving acoustic noise creates an “out-of-phase” signal that, when played back at the same time as the noise being generated, reduces and or cancels it out. U.S. Pat. No. 5,828,768 describes a multi-media computer having piezoelectric transducer panels, microphones and a sound card, configured to provide active noise reduction. The microphones are positioned in the internal walls of a desktop computer or to the inside of the display panel of a lap top computer and provide acoustic noise feedback to an electronic circuit that generates a noise cancellation sound that is broadcasted through the speaker to cancel fan, HDD, and floppy disk drive noise. The problem with this approach is that when acoustic noise is mixed with intended sound, the sound can get cancelled or reduced along with the acoustic noise because the electronic circuit may not be able to distinguish between the two. For example, under this approach when a HDD is used in a PTV, the intended TV sound would be cancelled along with the undesirable noise.
What is needed is an acoustic noise reduction method that can selectively reduce noise generated by the HDD while not affecting intended sound, or changing the form factor of the HDD.